Is Slow & Steady Actually the Best Way to Diet? (Calorie Deficits #2)

“Many people advise to lose weight at a steady and moderate rate, and recommend not cutting calories too low, in order to preserve muscle mass”.

That’s a line taken from an email I was sent a few weeks back. And it perfectly exemplifies a piece of supposed common sense.

And at first glance this makes some degree of logical sense, right?

With a slower the rate of weight loss, theoretically, you might expect to have more of that weight loss coming from loss of body fat as opposed to lean tissue. And the more aggressive you diet the greater the degree of muscle breakdown and the greater the risk of losing lean body mass. Both of which are true, but only to a certain point.

The real truth is, as usual, a lot more nuanced. Much more gray than black-and-white.

So whilst not the worst idea in the world, the idea that “slow and steady” is always the best approach to dieting is simply not correct. I feel that much of the recommendations that “slow and steady is the best policy” is simply a result of one of the following flawed assumptions:

Large calorie deficits will always lead to more muscle loss than mild deficits

Large calorie deficits will always cause more weight re-gain after the dieting period is over

Both are ‘kind of’ true, to some degree. But only to some degree. There is both research and anecdote of folks being able to lose weight rapidly on a large caloric deficit, whilst preserving muscle mass.

Defining a Large Calorie Deficit

It’s common to see a caloric deficit of 500 kcal/d prescribed as a moderate deficit in which weight loss should occur at roughly 1 lb (0.45 kg) per week. This is based on the loose assumption that 1 lb of body fat has 3,500 kcal of energy that can be metabolized to make up for that shortfall. Whilst in many cases this may be a decent approximation, it is flawed for many reasons. One, as mentioned earlier, is that the deficit will be made up for by metabolizing not only body fat, but glycogen and bodily proteins as well. However, I do not prescribe a 500 kcal deficit for a number of other reasons.

I believe that proportional caloric deficits should be prescribed (i.e. those set as a percentage of the individual’s maintenance caloric intake).

If you use absolute numbers of calories (e.g. 500 kcal) then how “aggressive” that diet will be is dependent upon the typical energy expenditure of the individual in question. For example, by using a 500 kcal deficit across the board, you can create a scenario where for one individual the diet is very mild and another it is extremely aggressive. Consider:

a large, highly-active male with significant muscle mass who maintains his weight on 5,000 kcal per day

a small-framed, sedentary female who maintains weight on 1,500 kcal per day

Despite using the same absolute deficit, in the above examples you are inducing caloric decreases of 10% and 33% respectively.

So if we go by percentage reduction, we then must decide what constitutes a slight, moderate, large, extremely large, etc. calorie deficit. You’re not going to find exact definitions that everyone goes by. However, others have put together ranges that likely serve well for our purposes. Lyle McDonald classified them as:

Small: 10-15% below maintenance

Moderate: 20-25% below maintenance

Large: anything bigger than 25% below maintenance

Really how “aggressive” a diet is can be viewed along a spectrum of the percentage drop below maintenance intake. You could also make the argument that you could rate the “aggressiveness” of a diet in a subjective manner, thus meaning it will vary from person to person.

Nevertheless, we’re just playing semantics at this point. The above classifications suit our needs for this article.

Additionally, it also seems that the initial amount of body fat someone has can impact the amount of fat loss they experience. Models produced by Kevin Hall suggest that those with more body fat will need a larger deficit than leaner people to lose the same amount of body fat:

“The resulting model predicts that a larger cumulative energy deficit is required per unit weight loss for people with greater initial body fat – a prediction supported by published weight loss data from obese and lean subjects. This may also explain why men can lose more weight than women for a given energy deficit since women typically have more body fat than men of similar body weight.”(Hall 2015)

Now, let’s revisit those two assumptions on which the “slow and steady” dieting philosophy is built:

Large calorie deficits will always lead to more muscle loss than mild deficits

Large calorie deficits will always cause more weight re-gain after the dieting period is over

Does a Large Deficit = Muscle Loss?

One theoretical reason centers around the impact of a caloric deficit on the muscle protein synthetic response. There is research to suggest that a caloric deficit likely reduces basal muscle protein synthesis (MPS) (Pasiakos et al., 2010) and it may reduce the sensitivity of MPS to feeding (Murphy et al., 2015)

Recently, data from a study headed up by Tom Longland out of Stu Phillips’ lab at McMaster showed that not only did young men (~ 23 y.o.) in an four week study not lose muscle mass despite a FORTY percent calorie deficit, they were actually able to increase muscle mass (+ 1.2 kg), when resistance training and a high-protein diet (2.4 g/kg BW) were used. (For more commentary you can check out this podcast episode with Caoileann Murphy who was part of Stu’s team at McMaster).

Just as an interesting side note, that high level of protein intake and thus higher per-meal doses of protein in the Longland et al. paper could be what allowed MPS to be maximized despite the deficit. Moore et al. (2015) previously pointed to a protein dose of 0.25 g/kg per meal as sufficient to maximize MPS when someone is in energy balance. In the Longland et al. study, the lower protein group (1.2 g/kg BW) were pretty much consuming this figure; 0.23 g/kg per meal. But as pointed out by Murphy et al., the deficit could reduce the sensitivity of MPS to that feeding. And so the high protein group were able to maximize the MPS response as they were consuming 0.48 g/kg per meal.

So we can see that large caloric deficits do not always lead to muscle loss (and in fact muscle can still be built), especially when we use adequately intense/novel training stimulus in combination with a high protein intake. Of course, taking into account the populations in such studies. It’s highly unlikely an advanced bodybuilder would build over 1kg of lean body mass in 4 weeks whilst in a 40% calorie deficit now isn’t it?

But that’s not to say advanced trainees cannot preserve/gain muscle in caloric deficits. We see that capacity over and over again in studies. It’s just a case that the harsher the deficit in already lean individuals carries a greater risk of muscle catabolism.

Do Large Deficits Lead to More Weight Re-gain in the Long-term?

Earlier we alluded to two assumptions that are the basis for believing slow and steady is always best.

Large calorie deficits will always lead to more muscle loss than mild deficits

Large calorie deficits will always cause more weight re-gain after the dieting period is over

Let’s now turn our attention to the second of those. Will a more aggressive diet mean that the dieter will be more likely to binge or over-compensate after the diet and therefore gain back more weight?

First let’s consider the obese.

A 2010 study looked at a 6-month lifestyle intervention and 1-year extended care program in obese women (~ 59 y.o.). In that intervention they were encouraged to reduce their caloric intake to a level that would predict a loss of 0.45 kg/week (~1 lb/wk). Then based on the women’s response to the diet over the first month, they were classified by weight loss; slow, moderate and fast.

Fast = weight loss ≥ 0.68 kg/week (n=69)

Moderate = weight loss 0.23 – 0.68 kg/wk (n= 104)

Slow = weight loss <0.23 kg/wk (n=89)

Not only did the fast weight loss group lose more weight during the 6 month intervention (as we would obviously expect), but one year after the intervention had finished they they were still in a much better position than the slower dieters. There were no significant group differences were found in weight regain between 6 & 18 months (2.6, 1.8, and 1.3 kg). And the fast weight loss group were 5.1 times more likely to have lost 10% of their bodyweight at the 18 month point than the slow weight loss group.

As should be clear by now, we always need to contextualize things and ask in what specific scenarios are we talking about. For illustrative purposes, here are two extremely different individuals to consider:

35% body fat, pre-diabetic, elevated fasting glucose and triglycerides, long history of struggling to lose weight

Natural bodybuilding competitor, currently 8% body fat and aiming to get to ~5%

How likely is it that both of these individuals would lose the same amount of lean body mass if we were to put them on an extremely low-calorie diet for a couple of months?

I think as a general rule of thumb, it’s prudent to consider that the leaner an individual is and/or the more importance placed on athletic performance, the more gradual the rate of weight loss should be and therefore the more moderate the deficit should be.

There are still exceptions to this “rule” however.

What About Leaner People? What About Athletes?

A study on Finnish track and field athletes highlights the effect of leanness (Huovinen et al., 2015). This gives a good insight as all the participants were National level athletes and between 20-35 years old. In the study they were split into two groups:

Large deficit group – 750 kcal deficit

Small deficit group – 300 kcal deficit (note: when actual diets were examined this group didn’t actually change intake from baseline so they didn’t actually diet! So it was really a maintenance group)

Despite being lean and highly active, the athletes on the large deficit lost predominantly body fat (almost 2 kg) with a small average fat-free mass (FFM) loss (-0.5 kg). But interestingly when you look at individual data points you see that the ones who were able to preserve fat-free mass were those who were over 10% body fat. Those who were sub-10% body fat lost more FFM.

Of course this is only one study. And of course it’s important to be aware that other data exists. But the reason I point to the Huovinen study is that is highlights a few things that I think are representive of conclusions we can draw from other data and personal experiences with lean individuals doing high levels of sport training:

Big deficits can certainly lead to FFM losses in athletes

However it’s also possible to have a large proportion of the weight loss coming from fat mass

The leaner the athlete, the greater the risk for FFM loss

We could go deep into the weeds on these points but that’s not really my intention in this article. Rather, I’d prefer to look at this pragmatically and ask “does it even matter?”

Does Muscle Mass Loss Even Matter?

This might sound like an idiotic question. I mean, why train so hard to add muscle mass if you’re just going to lose muscle once you start dieting?

Well we need to ask ourselves:

How much muscle is actually being lost?

How quickly will this return once the diet period is over and a nutrition/training program that supports growth is re-instated?

Are you a competitive bodybuilder prepping for a contest?

I would think that, again within the context of proper training and protein intake, that the answers are most likely:

Not as much as most people seem to think

Pretty damn quickly

Yes? Then LBM losses are a bigger deal, so diet slowly. No? Then you don’t need to be as big as possible at the end of the diet.

We could spend a whole other article getting into this. But thankfully we don’t have to. Much of the reasons why I don’t think losing some muscle mass during an aggressive diet is much of an issue, are essentially the same as Greg Nuckols highlighted in some previous discussions of myonuclear domain theory (for example in the first half of THIS POST or summarized HERE).

Essentially, yes you may lose some LBM during very aggressive dieting periods BUT:

If you combine a smart resistance training program with a sufficiently high protein intake, you’re already well on your way to mitigating as much of the losses as is possible

It’s easier to regain lost muscle mass than it is to build it in the first place. This is why the gains folks experience when returning to training after a lay off are relatively quick.

Aggressive dieting periods mean a shorter duration of time spent in a dieting state. So you can spend more of the year in a caloric surplus, which is good for gaining, performance and recovery (not to mention the soul!). More on this in the next article in this series.

Take Home Point

The purpose of this post is NOT to serve as a “pro-aggressive dieting” stance. Nor is it to push the idea that using large calorie deficits is “better” than more slight calorie deficits.

It is also NOT a thorough literature review. I’m aware there are conflicting studies. The reason the studies in this article were included is because they are representative examples of other research showing a few important things:

Large calorie deficits do not always mean muscle mass will be lost

Even advanced trainees and athletes can maintain/gain muscle during a deficit

Rapid weight loss does not always mean more weight will be regained

In some cases, aggressive dieting and fast weight loss can be the best option

To conclude, the point of this article is that rather than presume a certain method is always the best, we need to remain critical in our thinking and consider the various scenarios that could be applied.

Nothing in nutrition is ALWAYS the best option or THE one true way to success. Slow vs. rapid weight loss (or slight vs. large calorie deficits) is just another example.

[EDIT: Since writing this article, some of these topics were discussed on the podcast in episode 128 with Martin MacDonald. Listening to that is highly advised as an adjunct to this material]

In part 3 of this series, we’re going to dive into more practical applications of this. Looking at the pros and cons of aggressive dieting.